Energy consumption analysis for CO₂ separation from gas mixtures with liquid absorbents

CO₂ separation is an energy intensive process, and it plays an important role in both energy saving and CO₂ capture and storage (CCS) to deal with global-warming. CO₂ can be from different sources in a wide temperature, pressure and concentrations range. Meanwhile, new liquid absorbents are under-development to cost-effectively separate CO₂ from gas mixtures. All this makes it crucial to analyze the energy consumption for CO₂ separation from different streams and with different absorbents. In this work, the theoretical energy consumption of CO₂ separation from flue gas (CO₂/N2), lime kiln gas (CO₂/N2), biogas (CO₂/CH4) and bio-syngas (CO₂/H2/CO) was calculated. The results show that the energy consumption of CO₂ separation from flue gas is the highest and that from biogas is the lowest. If the CO₂ captured from flue gases was substituted by that from biogases, the energy saving would be equivalent to 28.13 million ton standard coal globally. The energy consumption of CO₂ separation from biogas using traditional absorbent of 30%MEA and new developed ionic liquids (ILs) was further studied, in which 1-ethyl-3-methy- limidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][NTf2]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide ([Hmim][Tf2N]) and 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([Bmpy][Tf2N]) were screened from 75 ILs. The energy consumptions of CO₂ separation using ILs are lower than those of 30%MEA and that of [Bmim][BF4] is the lowest in the four screened ILs. With a very low vapor pressure and high CO₂ solubility, it's promising to use ILs as absorbents for CO₂ separation.